1. Field of the Invention
The present invention relates to a machine vision system for detecting and recognizing objects, and more particularly to a machine vision system that is preferably used in traffic surveillance which enables an operator to select variably sized zones to be monitored and can detect vehicles at night and in all weather conditions.
2. Description of the Prior Art
Advanced traffic surveillance and control continues to be a major area of research. One principal area of research in traffic surveillance is that of vehicle detection. Classically, inductive loops located at strategic locations in the roadway have been used for vehicle detection. However, there are numerous problems with inductive loops, including sensitivity and the need to install them in the roadway, which are well known. In one manner improvement over loops, video cameras have been used as a more viable way to achieve vehicle detection. However, systems which employ video cameras generally require a human operator to interpret the images generated by the camera and are therefore undesirable because of the staffing and communication costs.
An alternative way to interpret video images that has recently been developed is through image processing or "machine vision." This technique uses a computer and software to analyze the roadway images the information needed for traffic surveillance and control. In spite of major efforts to develop a machine vision system for traffic surveillance and control, a workable device having the capabilities and performance required for practical applications has been elusive. The principal problems that have been encountered with machine vision systems for traffic surveillance have been (1) reliable operation under various weather and traffic conditions, (2) the arbitrary placement of multiple detection points in any configuration anywhere within the camera's field of vision, (3) automatic adaptation to a wide variety of roadway backgrounds, and (4) distinguishing between various objects such as cars, trucks, pedestrians or other objects.
As mentioned above, a problem that has been encountered in traffic monitoring and surveillance systems is the operability of the system under various weather and traffic conditions and at night. Many detection systems that use standard video cameras encounter problems when weather conditions become onerous and vision is blurred or at night when vision is reduced. Therefore, a traffic monitoring system is desired which can operate under all weather and traffic conditions.
One traffic surveillance system that has recently been developed employs machine vision for traffic detection, surveillance and control. This system is referred to as AutoScope and was developed at the University of Minnesota. The AutoScope vehicle detection system can detect traffic in a number of horizontal zones within the camera's field of view. An operator can specify these zones using interactive graphics by placing vertical detection lines along or across the roadway lanes on a television monitor displaying the traffic scene. The detection lines are placed vertically the television monitor showing the representation of the roadway lanes. Once the detection lines have been set, the monitor can be removed from the system. Thereafter, every time a car crosses these detection lines, a detection signal is generated by the AutoScope device.
This method of determining locations or zone within the camera's field of view is somewhat inflexible because the zones are limited to the full vertical height of the camera's field of vision. As a result, the selected zones in this system generally contain a much larger area than is actually needed to detect a vehicle or object within the zone. The unnecessarily large zones required in this system increase the amount of image processing required. Also, this limitation in zone selection limits the number of positions in which the camera may be situated.
The AutoScope system works such that every time a car crosses the one of the selected zones, a detection signal is generated by the device. This detection signal is similar to that produced by the standard loop detectors. Therefore, the AutoScope system detects the presence or passage of an object through one of its zones. The AutoScope system does not distinguish between automobiles, trucks, pedestrians, or other objects that pass through its zone. However, in many instances it is desirable to record the number and types of vehicles which pass through a given intersection. Therefore, it is desirable for a traffic surveillance system to be able to recognize objects that pass through its various zones.
In addition, many of the proposed traffic surveillance systems are somewhat large and bulky and therefore are inconvenient to set up. Therefore, it is desirable for a machine vision system to be incorporated into a single, self-contained apparatus to provide for convenience and ease of use.